The arylterpenoid compounds produced by the processes hereof have a 2,6-dimethylnonane backbone and are substituted at the 2-position by a lower alkoxy group, e.g., methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, etc. At the 9-position of the nonane chain is an aryl substituent from which the compound in part derives its name. The aryl group, usually phenylene, preferably contains at least one substituent group directly connected to a ring carbon atom. For best results the substituent group is located in the position para to the point of attachment to the nonane chain. Consequently, the compounds produced in accordance herewith may be represented by the structural formula shown in the aforesaid patent: ##STR1## wherein A is a C.sub.1 -C.sub.5 alkyl group, preferably ethyl, isopropyl, sec.-butyl, tertiary butyl; a C.sub.1 -C.sub.4 alkoxy group, e.g., methoxy, ethoxy, isopropoxy; a C.sub.1 -C.sub.4 thioalkoxy group, e.g., thioethoxy, nitro, or 3,4-methylene dioxy; more preferably A is in the para position, and most desirably A is in the para position and selected from C.sub.1 -C.sub.5 alkyl; R and R' are independently methyl or ethyl, preferably methyl;, R.sup.2 is a C.sub.1 -C.sub.4 alkyl group, preferably methyl or ethyl, more desirably methyl. These compounds will inhibit eclosion of flies and mosquitos by several modes of application including application directly to the larvae or pupae, application to the natural growth media such as animal feces, incorporation in the diets of livestock and poultry and by spray application in appropriate animal housing areas.
A method of preparing the above compounds is disclosed in U.S. Pat. No. 4,002,769 proceeding through an ylid (phosphorane) plus citronellal to form a diene hydrocarbon. This is partially hydrogenated to a monoene and later alkoxylated to yield the final product. More recently, the methoxy derivative of citronellal has become commerically available. The alkoxylation when performed early avoids the final alkoxylation step as described in the above patent.
Methoxy citronellal can be prepared from geraniol according to the following scheme: ##STR2## Geraniol/nerol can be produced from linalool according to the isomerization procedure described by Kane in U.S. Pat. No. 4,254,291. Linalool can be made from alpha-pinene by the following scheme: ##STR3##
A process for making arylterpenoid compounds may proceed by reacting methoxy citronellal with p-isopropylbenzyl magnesium chloride or bromide followed by dehydration and hydrogenation according to the following scheme: ##STR4##
Alternatively, instead of using methoxycitronellal, methoxycitronellyl chloride or bromide can be made and converted to the magnesium chloride or bromide (Grignard) and the latter reacted with p-isopropylbenzaldehyde, dehydrated, and hydrogenated or hydrogenolyzed to yield (I) above.
We have found a much shorter and less expensive route to the formation of arylterpenoid compounds of the type described in the aforesaid U.S. Pat. No. 4,002,769. The success of the procedure depends on the application of a surprisingly effective obscure, albeit known (See Tetrahedron Letters, Vol. 22, pgs. 85-88 (1981)), Grignard exchange reaction whereby a lower alkyl Grignard reagent is exchanged with 3,7-dimethyl-1,6-octadiene (dihydromyrcene) or its derivatives. This is distinct from the normal Grignard formation reaction from halides. The presence of a remote alkoxy group in the dihydromyrcene structure not only does not inhibit the reaction, but appears to have a positive effect on the conversion. We are able moreover, to start with relatively inexpensive alpha or beta-pinene or a mixture thereof, and in a very few steps produce (I) above, instead of using the more numerous and costly steps involved in U.S. Pat. No. 4,002,769 or alternative procedures such as mentioned above.